1. Field of the Invention
The present invention relates to an optical recording medium (e.g., an optical disk), and a reproducing method and apparatus using the same.
2. Related Background Art
Along with the progress in an information-oriented society, an amount of information is kept on increasing. Strong demand has arisen for a large-capacity information recording medium. Of all conventional optical recording/reproducing schemes, an optical recording/reproducing scheme for recording/reproducing information using light (light spot) capable of being focused within a very small area (e.g., an area having a diameter of about 1 .mu.m) is most popular because the information recording density can be much higher than a conventional magnetic recording/reproducing scheme. In a state-of-the-art optical recording/reproducing scheme, information is recorded on an optical recording medium as a change in physical quantity such as a change in crystalline state or maximum absorption. This change is read as a change in polarization plane or amplitude (intensity) as a physical quantity of light.
In the conventional optical recording/reproducing method, physical changes caused in a medium as information for the area of a light spot are of one kind, or even if they are of plural kinds read light is extracted as a change in only one of the physical quantities of light. For this reason, the minimum unit in information recording is one quantity per area of one light spot. So, the information recording density is limited to the magnitude of a light spot, which is of a size larger than a diffraction limit determined by a wavelength and the numerical aperture of a condenser lens. As a result, the information recording density cannot be higher than the diffraction limit.
As recent techniques for increasing the recording density, a confocal structure (ex. J. Broat, Jpn. Apl. Phys. Suppl. 28-3 (1989) 103), a V-groove optical disk (ex. M. Nagashima et. al., Proc. SPIE, 1656 (1992) 20), an MSR (K. Aratani et. al., Proc. SPIE, 1499 (1991) 209), a crosstalk canceler (ex. K. Kayanuma et. al., Proc. SPIE, 1316 (1990) 35), and the like have been proposed. Of these conventional techniques, the confocal structure is not practical because an amount of detection light must be sacrificed to sufficiently increase the resolution. The V-groove disk has a high manufacturing cost, and the recording scheme of MSR is limited to the magnetooptical recording only. The crosstalk canceler requires three beams in signal reproduction, and its optical system is complicated.